The present invention relates to rocket engines and, more particularly to a tubular rocket engine combustion chamber.
The rocket engine combustion chamber contains the combustion of pressurized fuel and oxidizer and the smooth acceleration of the combustion products to produce thrust. The oxidizer and fuel are introduced under pressure through the injector 10, such as that shown in FIG. 1, attached to the top of the chamber. The combustion products under pressure advance to a de Laval nozzle 12, where the internal profile converges to a throat 14. Here the expansion of the combustion products achieve sonic velocity. The convergent throat section is immediately followed by a divergent section 16. The combustion products are then further accelerated to many times the speed of sound depending on the profile of the divergent section, the oxidizer and fuel combination, the pressure of the combustion products and the external pressure. The acceleration of gases creates thrust for the rocket engine.
Regenerative cooled combustion chambers take part of the flow of cryogenic liquid propellant, usually fuel, to cool the walls of the combustion chamber. The coolant flows along the outside of the chamber through passages or tubes. The coolant recycles the waste heat to increase energy in the coolant. This increase energy in the coolant improves the efficiency of the cycle.
Regenerative cooled combustion chambers for rocket engines typically fall into three categories: milled channel, platelet, and tubular construction.
In a milled channel construction, grooves of varying cross section are cut into the exterior of a liner, which assumes the shape of a de Laval nozzle. A jacket is built up over the open channels or a cylindrical piece is slid on and vacuum compression brazed to the liner. The jacket resists the coolant pressure only.
A platelet construction is similar to a milled channel but divides the length of the liner into many smaller sections, which are then bonded together. A multiple piece jacket is then welded together over the liner and vacuum compression brazed together.
A tubular combustion chamber stacks formed tubes in the shape of a de Laval nozzle. The tubes contain the pressurized propellants for cooling the chamber walls and picking up waste heat to use in the cycle. The finished jacket assembly resists the pressure load of the combustion products only.
A tubular construction combustion chamber can be manufactured in two ways depending on its size. If the chamber is large enough in diameter to allow access, the tubes and braze material can be laid directly into a single piece jacket and furnace brazed.
Smaller chambers do not allow the use of a single piece jacket because access is limited to insert tubes inside a small diameter jacket. Assembly starts by stacking formed tubes on a mandrel in the shape of a de Laval nozzle. The tubes can be laid straight along the length of the mandrel or can be spiral wrapped around the mandrel. Braze wire, paste, or foil is inserted into all the cavities between the tubes. A multiple piece jacket is then added to the outside of the tubes. The jacket segments are then covered with overlapping strips between the jacket segments. The jackets and tubes are then furnace brazed together. The tubular construction chamber integrity depends on the quality of construction of the jacket and braze coverage for all joints between the tubes and the chamber manifolds and stiffening rings. Only X-ray or sonic inspection methods can accomplish inspection of the brazed tube to tube and jacket to tube joints. Repair of the brazed areas under the jacket is difficult. Failure of the combustion chamber can occur because inspection techniques were insufficient to identify areas of inadequate braze coverage.
The tubular construction chamber yields the lightest and most efficient chamber due to the larger heat transfer area and lower stressed tube cross sections. The tubular construction chamber integrity depends on the quality of construction of the multiple piece jacket and braze coverage for all joints between the tubes, jacket segments, and manifolds.